316
There have been various studies of the effects of calcium carbonate formation in the sea on
the level of CO 2 in the atmosphere over the timescales of the main geological cycles
(Chamberlin, 1898; Yolk, 1989) and of glacial-interglacial cycles (Berger, 1982; Dymond and
Lyle, 1985). All conclude that an increase in the ratio of carbonate-carbon to organic carbon
sedimentation will lead to an increase in atmospheric CO2, due to the assimilation of
bicarbonate:
Ca 2 + + 2HC0 3 - = CaC0 3 + CO 2 + H 2 0
The details of the mechanisms in terms of changes in the rates of exchange of C~ between
the atmosphere, surface ocean and deep ocean are uncertain, and for this reason, studies of
the effects of coccolithophore productivity on the state of the CO 2 system in surface ocean
waters are needed.
% coc0 3 (I)
Or-~IO~~20~~T-~~r-~~r-ro~_
/
20
40
100
10
I
,
\
\
It
/
\
\
A
I
I
I
,
A
I
I
I
I
I
I
/
/
2
3
4
5
6
10' FOtom,n,'.rO(9 d wi r' (A)
- - - '" IO.CXXl y.
Figure 10. Vertical distributions of calcite (% dry weight), coccolith abundance (g"') and foraminifera (g.l) in
sediment core 850701 from the Rockall Trough, NE Atlantic (5rOO'N, 12°0I'W, water depth 2130m).
Approximate dates before present are based on the occurrence of sinistral form of the foraminifera
Neogloboquadrina pachyderma.